For the prepositional meanings “over and above, in addition to” and “except” besides is preferred, especially in edited writing: Besides these honors he received a sum of money. We heard no other sound besides the breaking surf. However, beside sometimes occurs with these meanings as well.

beside

prep.

Old English be sidan "by the side of" (only as two words), from be- + sidan dative of side (n.). By 1200, formed as one word and used as both adverb and preposition. The alternative Middle English meaning "outside" led to the sense preserved in beside oneself "out of one's wits" (late 15c.).

beside oneself

Undergoing a surge or transport of emotion, esp of anger; half-crazy: She was beside herself when she found out he was cheating/ He was beside himself with despair(late 1400s+)

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.Copyright (C) 2007 by HarperCollins Publishers.Cite This Source

Idioms and Phrases with beside oneself

beside oneself

In a state of extreme agitation or excitement, as in She was beside herself when she found she'd lost her ring, or Peter was beside himself with joy—he'd won the poetry award. This phrase appears in the New Testament (Acts 26:24): “Paul, thou art beside thyself; much learning makes thee mad.”
[ Late 1400s
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